Attrition mill apparatus



Feb. 23, 1965 c. D. FISHER 3,170,649

ATTRITION MILL APPARATUS Filed April 16, 1962 4 Sheets-Sheet 1 INVENTOR i C. Daggaial .Fzlsher Feb. 23, 1965 c. D. FISHER 3,170,649

ATTRITION MILL APPARATUS Filed April 16, 1962 4 Sheets-Sheet 2 INVENTOR CDonaJd Fisher 7 m TTORNEY c. D. FISH-ER ATTRITION MILL. APPARATUS Feb. 23, 1965 4 Sheets-Sheet 4 Filed April 16, 1962 INVENTOR. c Paw/24D PAS/YEA nrra/ver United States Patent.

3,170,649 ATTRITHUN MEL APPARATUS Chester Donald Fisher, Muncy, Pa, assignor to Sprout, Waldron & Company, Inc., Muncy, Pin, a corporation of Pennsylvania Filed Apr. 16, 1962, Ser. No. 137,745 5 Claims. (Cl. 241-292) This invention relates to rotary attrition mill apparatus in which attrition or refining or grinding action is obtained by passing material to be treated between the opposed faces of two cooperating and relatively rotating discs having grinding or refining or attrition plates or surfaces thereon and, more particularly, to an arrangement in such apparatus for preventing or compensating for axial deflection of such rotating discs as may be caused by centrifugal or other action of the grinding or refining or attrition plates thereon. This application is a continuation-in-part of co-pending application Serial No. 9,758, filed February 19, 1960, now Patent No. 3,038,673.

In attrition mills generally of the character to which this invention relates, as well understood, one or more rotating discs are provided for cooperating attrition action with either another rotating disc or a stationary disc arrangement. In each case, the material to be treated with the grinding or attrition or size reduction action desired is introduced, usually in slurry or other fluent form, between opposed cooperating surfaces of the relatively rotating discs, and the severity and other characteristics of the treatment desired are controlled or determined by the spacing between the discs and by the particular configuration of the working surfaces thereof.

Such apparatus may comprise quite large and expensive machinery (frequently with discs three or four feet in diameter and requiring three thousand or four thousand horse power), yet it may be desired to operate such apparatus with relatively slight spacing between the coopcrating working surfaces of the discs and with adjustment within close tolerance limits and under substantial operating pressure applied over the whole disc surface. Actually, as will be understood, even inadvertent variations of spacing of. but a few thousandths of an inch-whether caused by disc deflection or otherwisemay result in undesired variation or non-uniform treatment results of the material being treated and/ or may cause actual mechanical disadvantages in the operation of the apparatus. Thus, even extremely minute misalignment variations adjacent the center of such rotating discs several feet or more in diameter are greatly magnified at the operating peripheries of such discs, and such deflections or misalignments can readily be disruptive of the desired close working spacing between the discs in one direction or another, whether such deflections or misalignments arise from centrifugal or other mechanical forces or hydraulic or heat expansion factors or otherwise.

Conventionally, if not universally, the actually working or attrition surfaces in such apparatus are provided by segmented attrition plates bolted or otherwise replaceably affixed to the opposed facing surfaces of the discs, and this situation obtains generally whether the apparatus comprises two counter-rotating discs, as in said co-pending application, or a single disc cooperating in working relation with a stationary or non-rotating disc or head, as in Patent No. 2,226,429. As will be understood, such replaceable plates are desired both to provide for replacement of the working surfaces as they become worn as well as for interchanging different patterns or textures of working surfaces for different jobs and without requiring major disassembly or rebuilding of the entire apparatus.

Particularly with larger diameter discs operating at relatively high speeds and with heavy attrition plate segments aflixed to one face of the discs, a substantial moment of centrifugal force may be introduced and acting on the centers of gravity of the attrition plates tending to deflect the rotating discs at the peripheries out of true alignment with the transverse plane in which the discs should be rotating. If such deflection amounts to only a few thousanths of an inch, it may nevertheless produce significantly disadvantageous results in the treatment desired when operating the discs with very close working spacing therebetween.

If it is attempted to compensate for such deflections by, for example, making the working surfaces of the attrition plates non-planar and/or beveled or tapered so that the working surfaces will be desirably parallel when the apparatus is up to speed and the above noted deflections are occurring, other difficulties may be experienced such as actual touching or clashing of the plates when the machine is at rest or operating at slow speed and where such deflections are less pronounced. As a result, it may be necessary to widen the spacing between the plates before stopping the apparatus or slowing it down and/or to start the apparatus with wider spacing than is ultimately desired. Especially may such difliculties be encountered in situations where the attrition plates are directly retained against centrifugal force by an overlying peripheral flange on the rotating discs against which outer edges of the attrition plates are forced during rotation of the apparatus.

According to this invention, however, an arrangement is provided whereby such centrifugally-engendered forces tending to deflect the rotating discs of rotary attrition mill apparatus out of the desired plane of rotation are prevented or compensated for on the discs themselves and in a manner to accommodate a variety of different attrition plate segments of different designs with substantially complete or continuous compensation, yet without excessively or undesirably increasing the weight or thickness of the disc itself or the power requirements for maintaining rotation thereof and in a manner which does not have an undesired agitating or power-wasting effect on liquid slurry contacting the back side or surface of the discs during operation of the machine. Such arrangements may include, in accordance herewith, overhanging counter-balancing structures at the periphery of the disc and on the back or non-working surface thereof, integrally formed with the disc, for engendering an opposite and substantially equally counter moment of deflecting force against that engendered by the attrition plates themselves for maintaining the entire composite rotating structure substantially in static and dynamic running balance.

With the foregoing and other objects in View, this invention will now be more particularly described, and other objects and advantages thereof will be apparent from the following description, the accompanying drawings, and the appended claims.

In the drawings:

FIGS. 1 and 2 are elevation views of apparatus embodying and for practicing this invention from, respectively, the side and inlet or feeding end thereof;

FIG. 3 is a vertical axial section through apparatus of FIGS. 1 and 2 and taken along the line 33 of FIG. 2;

FIG. 4 is a partial vertical axial section on a larger scale showing a portion of the apparatus of FIG. 3 with the invention here applied thereto;

FIG. 5 is an axial section on a somewhat larger scale of one of the rotating discs of the apparatus in FIG. 3 along the line 55 of FIG. 6; and

FIGS. 6 and 7 are plane views of, respectively, the back and working faces of the rotating disc of FIG. 5, but with attrition plate segments in place thereon.

As noted, an arrangement embodying and for practicing this invention is readily applied to or embodied in rotating attrition mill apparatus having but a single rotating Q3 disc for working relation with an opposed non-rotating attrition surface, although the particular embodiment indicated in the drawings for purposes of illustration includes two rotating attrition discs, each of which embodies the deflection-compensating arrangements in accordance herewith.

Thus, referring to the drawings, in which like characters of reference designate like parts through the several views thereof, apparatus embodying and for practicing this invention is generally illustrated in FlGS. 1 and 2 as having a base for supporting the apparatus and, par ticularly, the main housing and support frame indicated at 11. Base it also forms an aligned support for drive motor 12 for driving one rotating disc, as will be later described, through a coupling 13, and another drive motor 14 is provided for driving the other rotating disc through coupling 15 and gear train or other power transmission means in housing 16, with motor 14 being mounted on support 17 as indicated. A hand Wheel 18 is shown as part of the means for controlling and adjusting axial spacing between the rotating discs, and the control panel for operation of the machine is indicated generally at 19.

A generally cylindrical housing for the rotating discs themselves as indicated at 20 and as having a generally circular end closing plate 25. An inlet chute is mounted at the center of plate 25, and contains feeding mechanism such as a screw feeder mounted on shaft 31 separately driven by drive means in housing 32 for receiving material to be treated from inlet 30 and for feeding the material into the eye or central area of the discs within housing 26. A discharge 35 is indicated in the lower portion of housing 24 for the discharge of material after treatment by the discs within housing 20, although, as will be understood, the angular positioning of discharge 35 may assume any one of a variety of positions. Preferably, housing 29 overhangs the end of base It so that discharge 35 is freely beyond the area of the base.

As noted, inlet 30 and its appertaining feeding apparatus 31, 32, etc., all mounted directly upon and supported by end plate 25, which is in turn mounted on housing 2t] and preferably bolted thereto. If desired, two pairs of pin hinges 38 and 39, one pair at either side of the apparatus, are provided so that plate 25 may be swung open to either side for access to housing 2%. As will be understood from the foregoing then, by unbolting end plate 25, it, and all the various apparatus directly mounted thereon, can be swung out, on either pair of hinges 38 or 39. from either side, to give unrestricted access to the interior of housing 2.9 and to the discs therein. It should also be noted that such access is frequently desired for inspection or cleaning of the discs and/ or for changing the attrition plates thereon, and is accomplished according to this arrangement of apparatus without the necessity of uncoupling or disassembling any of the main drive means or bearings and even without the necessity of opening or having access to the main frame in housing 11 or the various main drives or interfering with whatever piping or conduit connections there may be associated with discharge 35.

Within housing 29 are two opposed rotating discs 40 and 45. Disc is mounted on and driven by shaft 50, while disc 40 is mounted at the periphery thereof on spider 55, as by lugs 56 and bolts 57. Spider 55, in turn, is mounted on and driven by a quill 60 positioned coaxially around shaft 50.

Referring now to FIG. 3, quill 60 includes an end portion 61 of enlarged diameter to be supported for rotation as by anti-friction bearings 62 outside thereof. The adjacent end of shaft 50 is supported for rotation within enlarged end portion 61 of quill 63 as by anti-friction bearings 63. The opposite end of quill 66 is supported by thrust bearings '79, and the opposite end of shaft 5%, preferably having a reduced diameter portion '71, is supported by thrust bearings 72. It should be noted that the main frame or housing section 11 of the machine includes a generally cylindrical wall portion '75 extending therealong, the interior of which can be finished or bored to accurate cylindrical dimensions. It is within this support that are fitted bearing block 76 for anti-friction hear ing 62 as well as bearing blocks 77 and 78 for thrust bearings 76 and 72. In this'manner, with bearing blocks '76 and 7'7 fitting in a cylindrical support for quill 6t) and with bearing 63 fitting within a cyindrical bore in quill 60 and bearing block '78 fitting within bearing block '77, the mounting of all the bearings, with their cylindrical bearing blocks, into cylindrical bores provides a readily achieved close tolerance means for maintaining the coaxial alignment of quill 6t shaft 59, spider 55, and both rotating discs 4 and 45, and virtually independently of misaligning deflections which might otherwise occur if the shafts were independently supported at such spaced points from a floor or base.

As previously noted, shaft 5i), carrying disc 45, is driven for rotation by motor 12 through coupling 13, and quill 69, carrying spider 55 and disc 46 is independently driven for rotation by motor 14 through coupling 15 and the power transmission which may satisfactorily comprise a gear train in housing 16 including gears 80 and 81 mounted on shafts 82 and 83, the latter of which is driven through coupling 15. Meshing with gear 81 is another gear 84 directly keyed to quill 6% for the driving thereof. It should also be noted that a labyrinth seal is preferably provided in front of anti-friction bearing 62 and between the rotating spider 55 and the stationary Walls, and a similar labyrinth seal is provided in front of bearing 63 between the bore of quill 6t and shaft 50, as indicated. Additional packing may also be provided on a rim or flange 85 of the back face of disc 45 cooperating with an offset portion as indicated on spider 55.

A plurality of integral or overhanging segments 36 on the back face of disc 45 adjacent the outer periphery thereof and a similar plurality of segments 87 on the back face of disc it? are provided, as explained in more detail below, for the deflection-compensating effect in accordance herewith. Also, as will be described later, se mented and/or annular attrition grinding or refining plates 90 and 91, having on their exposed surfaces serrations or grooves or other surface design to accomplish the particular attrition or refining function, are bolted to the respective inner faces of discs 49 and 45, respectively, to provide the annular attrition surfaces to accomplish the desired treatment of material as it is forced therebetween.

As previously noted, material inlet 3-0 and feeding mechanism for feeding material into the apparatus are all mounted on end plate 25. Inlet chute 30 leads to a generally cylindrical horizontal housing or passage leading through end plate 25 and defined by cylindrical wall 95 which extends into and through a central opening in disc 40. Feeding means, such as a conventional screw feeder 100, mounted on shaft 31, which is supported by hearing blocks 101 and 192 in feeding housing 32, is provided to receive material to be treated from inlet chute 30 and conducting it horizontally directly and positively into the central opening or eye of disc 40. Screw 160 is separately driven, as by motor 103, acting through V- velt drive 104, to feed the material to be treated into the apparatus at the desired rate. Preferably a fiinger nut having a plurality of vanes 105 is affixed to the end of shaft 5t against the hub 46 of disc 45 to begin to give the material being fed by screw 1% a circular direction for radially outward fiow thereof, under the action of centrifugal force, between discs 40 and 45 and the treating or attrition plates 90 and 91 mounted thereon. As will be understood, the rotation of discs 40 and 45 provides centrifugal force for pumping the material to be treated radially outwardly to pass between attrition or refining plates 90 and 91 for action on the material therebetwecn, to be discharged outwardly from both discs into housing 20 and further agitated by passing through the several spaced terial being fed therethrough, a function of the maintained spacing between the coacting surfaces of plates 90 and 91. Such spacing is adjusted and controlled and maintained by the axial positioning of shaft with respect to axially fixed quill and, consequently, of the disc 45 with respect to the cooperating and opposed inner face of disc 40.

The provision of such axial control and adjustment of spacing in the illustrated apparatus is indicated and disclosed in somewhat more detail in said co-pending application noted above, but may be generally illustrated here. Thus, thrust bearing for quill 60 and the appertaining bearing block 77 are axially permanently fixed within the supporting frame 75. The axial positioning of quill 60 with respect to bearing 70 is similarly fixed, as by ring threaded on the end of quill 60 to form an axial abutment for the portion 116 of the bearing race of bearing 70 which rotates with quill 60. Extending from the block 77 is a cylindrical sleeve 120 Within the main cylindrical frame 75, and axially slideably mounted within sleeve 120 are runners 121 which carry bearing block '78 for thrust bearing '72. It is to be understood that, although the radial or concentric alignment of thrust bearing 72 is maintained by mounting bearing block 78 on runners 121 within cylindrical sleeve 120 mounted within cylindrical frame 75, bearing block 78 is free to slide axially within sleeve 121). The axial positioning of the rotating portion 125 of the race for thrust bearing 72 with respect to shaft 50 is maintained by positioning race 125 on the reduced diameter portion 71 of shaft 50 between a shoulder 126 and a threaded ring 127 on the shaft so that axial movement of bearing block 78 will provide corresponding axial movement of shaft 50 and, of course, disc'45 carried thereby.

Such axial movement in one direction (e.g., to the left in FIG. 3) is provided by fluid pressure cylinders (not shown) mounted on the end closure plate 131'for main frame 75. Such cylinders, in known and well understood manner, have operating therein pistons which, upon introduction of fluid pressure therebehind, act through piston rods to urge runners 121 and bearing block 78 to the left in FIG. 3, thus moving shaft Sil to the left and moving rotating disc 45 closer to rotating disc 40. As a means of adjusting or limiting the extent of movement of shaft 50 to the left under the action of such fluid pressure cylinders, end plate 131 is provided with a flange within which is mounted for rotation worm gear which is threadably connected with sleeve 146 mounted around and for axial sliding movement with respect to an inner sleeve 147 surrounding reduced diameter portion 71 of shaft-50 and connected directly to bearing block 78 of thrust bearing 72. Inner sleeve 147 extends axially beyond sleeve 146 and carries at the right end thereof a threaded ring arranged to abut against one end of sleeve 146 as thrust bearing 72 and shaft 50 move axially with respect to the axially fixed end plate 131 and worm gear 146.

A worm 150 is mounted on shaft 151 and the rotation thereof is controlled by hand wheel 18 in such manner, as will be understood, that rotation of hand wheel 18 positions sleeve 146 in a specific axial positioning (through rotation of worm gear 145 and the threaded connection therewith of sleeve 146). Under such circumstances, and for any given axial positioning of sleeve 146, the extent of movement of shaft 50 to the left in the drawing under the action of fluid pressure cylinders 130 is limited by the abutment of ring 148 against the right hand end of sleeve 146, thus providing the desired adjustment and maintain- 6 ing the control of the spacing between the treating surfaces of plates 90 and 91 mounted on rotating discs 40 and 45, all as disclosed in somewhat greater detail in the above mentioned co-pending application.

Referring more particularly to FIGS. 4-7, the placement and arrangement of attrition plates 99 and 91 on the respective rotating discs 40 and 45 is indicated in somewhat more detail. Thus, the plates themselves are shown (in FIG. 4) as including attrition grooves or ridges for treating or working on the material passed between the spacing and cooperating working surfaces of plates 90 and 91. Also, the plates are provided, in known manner and as indicated in FIG. 7, as separate segments, each of which is bolted or otherwise aflixed to the working faces of discs 40 and 45 as by bolts 181, 182, threaded into bores 183, 184, etc., to form an annular working surface on the discs. As indicated in FIGS. 4 and 5, an annular recess 135 is provided on disc 45 to accommodate the various segments of plates 91, which recess is defined by outer peripheral rim 199 and inner circular rim 191, in such manner that the plates 91 are accommo dated in recess and between inner and outer rims 199-191 during rotation of the machine with bolts 182 merely holding the plates into recess 185 but without otherwise notably absorbing the centrifugal force engenered by the heavy plate 91 during rotation of disc 45.

That is, the centrifugal and other mechanical forces acting on plates 91 are withstood primarily if not entirely by edge flange on disc 45, rather than by bolts 182, and substantially the same situation occurs regarding the other rotating disc 40, where an annular recess is provided between outer rim 196 and inner rim 197 between which segments of plate 99 are held in position by bolts 181 in threaded borings 183.

' As will be apparent from the foregoing, as discs 40 or 45 rotate at high speed, the weight of plates 91) and 91 in recesses 195 and 185 generates a substantial radially outwardly directed centrifugal moment of force bearing strongly against the =outer edge flanges 190 and 196. Thus, the radially outwardly directed moment of centrifugal force (occurring independently for each of the various segments of plates 91, weight of which are shown in FIG. 7) bears directly against edge flange 190 of rotating disc 45 and with sufficient force to induce actual deflection of disc 45 toward the right in FIG. 4 and out of planar alignment during high speed rotation thereof.

Such deflection of disc 45 has a tendency to tilt the working face of plate 91 toward the right so that peripheral portions thereof will be further separated from the cooperating working face of plate 90 than are inner portions. Similar deflections also occur with rotating disc 40, because of centrifugal forces acting on plate segments 90, and may be more pronounced because of the open center and lack of hub structure in disc 49 as shown. Since the periphery of disc 40 is held by elements 56, such deflections tend to cause the radially inner and unsupported portions to deflect to the right and toward disc 45, and further renders non-unifonm the desired spacing between the working faces of plates 99 and 91. The extent of such deflections, of course, will vary with the centrifugal force exerted on plates 90 and 91, which in turn are functions of the diameter of the discs and the speed of rotation thereof. Accordingly, the higher the speed of rotation, the more non-uniform separation at the radially outer portions of plates 90 and 91 will become apparent.

Attempting to correct for such deflection by forming the cooperating working faces of discs 90 and 91 to be non-parallel when the apparatusis at rest (as also indicated somewhat in FIG. 4) may temporarily compensate for such deflections of the discs when the machine is rotating at high or working speeds, but may present a further problem in starting up or stopping the apparatus. Thus, substantial bevelling or bosoming" of plates 90 and 91 to retain or return to the desired parallel relation at high speed of operation also creates the opposite effect or relationship of the plates when the machine is stoppedi.e., the radially outward portion of the plates will be closer together than the radially inner parts. In such a situation, the running clearance desired between the opposed faces of plates 90 and 91 at full operating speed may actually be less than the bevelling or bosoming required to compensate for deflection. In such event the plates must actually be backed off or separated while running and prior to stopping the apparatus and/or be set at more than the desired spacing or separation when the apparatus is started and until it is brought up to speed in order to avoid'actual clashing or contacting of the plates at slower speeds with, obviously, disadvantageous and possibly destructive results.

Although such deflections may appear to be relatively slight, they create a very real dfliculty. For example, even with lighter plates 90 and 91 and rotating disc diameters of less than three feet, deflection-s from this particular centrifugal force cause may be routinely as much as .031", which deflections are, obviously, even more pronounced with discs such as 40 having an open annular central eye portion and/ or such an open portion including radial spokes as occurs in many constructions. Even with heavier types of apparatus with discs such as 45 up to 36" or 42" or 48" in diameter and correspondingly heavier construction, deflections of at least .006" to .10" are routinely encountered. Although such deflections are actually only in thousandths of an inch, they represent a significant proportion of the desired close tolerance spacing between the working faces of plates such as 90 and 91 in routine uses of attrition mill apparatus such as this in, for example, the refining of paper pulp fibres.

Presumably successful results might be achieved merely by increasing the heaviness of construction of the rotating discs 40 or 45 and/or by including in the back surfaces thereof stiffening ribs or spoke arrangements. From the standpoint of efficiency of operation and economy of manufacture, such extra heavy construction is definitely not preferred. Nor is it'desired to include on the back surfaces of the discs spokes or other radially directed discontinuities or ribs which would serve to agitate whatever liquid material is within housing 20 since such results merely tend to increase and waste horse power required to drive such spoke arrangements through the surrounding liquid slurry in accordance with the well understood laws of hydraulics.

In accordance with this invention, however, such deflections are satisfactorily prevented or compensated for, and without an extra heavy construction or the provision of protruding rigidifying elements on the back faces of the discs, by providing peripheral overhung compensating weights or counter-balance means such as 86 and $7, specifically dimensioned and positioned to engender a moment of centrifugal force oppositely axially directed to the deflection-producing force above noted and en gendered by plates 90 and 91 during high speed rotation of the apparatus.

Thus, considering rotating disc 45 as illustratively indicative of solid rotating discs generally in either double disc attrition mills as shown in the drawings or single disc mills as in Patent No. 2,226,429, counter-balancing weight 86 is formed, preferably integrally with disc 45, at the peripheral edge portions of the back side of the disc. As indicated in FIG. 6, counter-balances 86 are not continuous all around the disc, but are separated or subdivided by slots 200 to interrupt the strength of counter-weight 86 and insure its arrangement as simply a plurality of overhung masses on the back of disc 45. Satisfactory results are achieved if slot-s 200 substantially coincide with the meeting edges of the various plate segments 91 bolted on the front side of disc 45 (see FIG. 7) so that, effectively, there is provided on the back side of disc 45 a plurality of separate masses 86 substantially equal in number to the segments of plates 91 bolted to the face of the disc. Additionally, slots or notches 200 are primarily for the punpose of interrupting continuous strength angularly around disc 45, so they can be quite narrow and thus avoid the situation noted above regarding widely separated projections or ribs on the back side of disc 45 and undesired agitation or other hydraulic interference thereof with any liquid in the apparatus.

As will be apparent from the foregoing and consideration of the drawings, as rotating disc 45 with plates 91 thereon comes up to speed, a substantial moment of centrifugal force is generated with regard to the center of gravity of each of the segments of plates 91, urging such plates radially outwardly against flange 199, thus generating a turning moment of force about the center line of flange tending to deflect the peripheral edge of disc 45 to the right in the drawings. In accordance herewith, however, the overhung masses of counter-weights 86, as correlated to the size thereof and location of the center of gravity thereof with respect to the axis of disc 45, are similarly subject to the action of centrifugal force tending to urge counter-weights 86 radially outwardly. Because of the integral attachment thereof to the face of disc 45, however, this moment of centrifugal force also results in a turning moment about the peripheral edge of disc 45 tending to deflect disc 45 to the left in the drawings and counter to the opposite force generated by plates 91.

To achieve the compensating effect desired in accordance herewith, it is thus necessary merely to arrange the dimensioning and configuration of counter-weight 86 such that the centrifugal force produced by this counter-weight times the distance from the center of gravity thereof to the center line of disc 45 is substantially equal to the centrifugal force arising from plates 91 times the distance from the center of gravity thereof to the same center line of the disc. As noted, this compensating configuration is further simplified if the number of counter balancing masses 86 around disc 45 (as determined by the number of slots 200 therebetween) is equal to the number of separate plate segments 91, in which event the dimensioning and designing is simplified.

It has also been discovered that neither the mass nor the center of various plate segments 91 are appreciably changed beyond limits of significance here by the provision of a wide variety of different serrated or ridged working surface patterns on the plates. Even if this were not the case, however, the mass and effective center of gravity of various different styles or designs of plates 91 can further be effectively controlled within wide limits, by the configuring and dimensioning of the various weightsaving recesses or hollows 201 conventionally cast into the rear or non-working surfaces of plates 91 and/or by the placement and dimensioning of strengthening ribs 202 therein. Indeed, satisfactory results have been achieved in accordance herewith and productive of satisfactory operation free of all the above noted difficulties or disadvantages even when the deflecting moment of force caused by the plates is not exactly or completely compensated for by counter-weights 86, provided a substantial amount of the plate-generated deflecting moment is compensated for or offset within the range of at least 50% and preferably 75-90%.

For example, assuming that the effective center line C of disc 45 (FIG. 5) designates the line of plane about which undesired turning moments will occur, the designlng of a series of compensating masses 86 for the disc is readily accomplished in accordance herewith. Thus, 1n a 42" diameter disc the moment of centrifugal force generated by the plates at say 1200 r.p.m. may be about 316,000 inch pounds where the center of gravity of the plates 91 is 1.5" from the center line C. About 60% compensation for the undesired deflection caused by such moment of centrifugal force is achieved by forming counter-weights 86 generally configured as in FIG. 5 and with the centers of gravity thereof about 1.25" from center line C and at about 19.15" radius, and where the aggre gate weight of overhanging mass of metal in the counterbalancing elements is only about 195 pounds. In a similar construction in apparatus having disc 45 of 48" in diameter, the moment of centrifugal force of plates 91 to be compensated for may be around 490,000 inch pounds, of which as much as 79% can be balanced or compensated for by forming elements 86 having an added weight or mass of only about 414 pounds, in addition to the weight of disc 45 without such compensating elements 86, by forming such counter-balancing masses 86 with centers of gravity about 1.125" from the center line C and on about 20.3" radius.

As noted above, a similar compensating arrangement is applied to disc 40, at least in the types of apparatus having two rotating discs. In such cases where disc 40 is completely open in the eye as illustrated, the deflection compensation in accordance herewith may be even more important. As will be understood, the dimensioning of counter-balancing elements 87 for disc 40 is accomplished in substantially the same manner, and also with the element 87 being-discontinuous around disc 40, as previously described with regard to elements 86 on disc 45. Thus, assuming a thickness of disc 40 of about 2" and a diameter of about 42" to the radially outer edge of plate 90, the deflection-producing moment of centrifugal force of the plates 90 may be about 370,000 inch pounds, for which about 90% compensation is achieved with elements 87 provided in the manner illustrated in FIG. 4 and including an aggregate extra weight of about only 225 pounds with elements 87 being provided having the centers of gravity thereof approximately spaced 1.7" from the disc center line and on a radius of about 21.3. For a similar disc 40 in a 48" diameter mill, the plates 90 may develop a moment of centrifugal force of about 570,000 inch pounds and about 91% compensation is achieved in accordance herewith with an aggregate mass of counter-balancing elements 87 of about 290 pounds positioned with the center of gravity thereof about 1.7" from the radial center line of disc 40 and at a radius of about 25.7".

As will be apparent from the foregoing, an arrangement is provided in accordance herewith for correcting or balancing or compensating for deflecting moments of force generated by centrifugal forces acting on the various segments of attrition plates 90 and 91 and urging plates outwardly against restraining flanges or rims 190 and 196. Although complete compensation is readily accomplished by the appropriate dimensioning and placement of counter-balancing elements 86 and 87, satisfactory results are achieved in accordance herewith if only a substantial or preponderant deflecting centrifugal force is compensated for. Indeed, because of space limitations imposed by the otherwise conventional design considerations on apparatus of this character, less than complete compensation may actually be preferred in view of the smaller size and weight of counter-balancing elements 86 and 87 thus required. As will be understood, actual deflection is completely avoided if suflicient of the deflecting force is balanced to lower the unbalanced portion thereof to within the limits of rigidity of the disc construction.

Furthermore, the advantages of this invention are achieved without substantially altering the basic or complete design of the various operating portions of the apparatus and without undesirably increasing the cost or complexity of the manufacture in accordance herewith, particularly since the overhanging counter-balancing masses are readily and preferably integrally formed or cast in the manufacture of discs 40 and 45, and the various radial slots 200 readily formed therein. By utilizing a configuration as indicated with the slots 200 being fairly narrow, the total area of the back face of the rotating discs subject to hydraulic pressure from liquid material being treated in the apparatus is not notably increased, nor are other hydraulic or power wasting difficulties introduced as might be the case if more widely separated weights or ally independently bf the speed of rotation of the discs.

and the centrifugal deflecting which might be induced thereby, and whether the apparatus involves but a single rotating disc cooperating with a non-rotating opposed working face or whether there are two rotating discs as in the illustrated embodiment.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In apparatus having a rotating disc on one face of which are mounted a plurality of separate plate elements to be maintained in close tolerance spacing relative to a cooperating element of said apparatus and in which said plate elements tend to be axially deflected out of said close tolerance spacing, the improvement which comprises counterweight means on the opposite face of said disc, said counterweight means comprising an annular smooth-surfaced counterbalancing weight on said opposite disc face, said weight having slots therethrough for the subdivision thereof into a plurality of counterweight masses corresponding in number to and respectively 0pposed from said separate plate elements, said plate elements and said counterweight masses giving rise to substantially equal and opposite centrifugal forces during rotation thereof, the centrifugal forces on the counterweight masses counteracting the centrifugal forces on the plate elements to prevent axial deflection of the disc during rotation thereof.

2. In apparatus having a rotating disc operating substantially immersed in a fluid material, one face of which disc is to be maintained in close tolerance, spacing relative to a cooperating element of said apparatus and in which said one face tends to be axially deflected out of said close tolerance spacing, the improvement which comprises counterweight means on the opposite face of said disc subject to centrifugal forces during rotation thereof for effecting a counteracting axial force on said disc to prevent axial deflection of said one face, said counterweight means presenting a substantially smooth uniform surface to said fluid material around said disc to avoid agitation thereof and hydraulic resistance in passing therethrough during rotation of said disc. I

3. In apparatus having a pair of parallel rotating discs, the adjacent faces of said discs to be relatively maintained in close tolerance spacing, and wherein said adjacent faces tend to be axially deflected out of said close tolerance spacing, the improvement which comprises counterweight means on the opposite faces of each said disc and subject to centrifugal forces during rotation thereof for effecting a counteracting axial force on each said disc to thereby prevent the axial deflection thereof and thus maintain the close tolerance spacing of the adjacent disc faces.

4. Apparatus as claimed in claim 2. in which a plurality of separate plate elements are mounted on said one face of said disc, and wherein said counterweight means comprises an annular counterbalancing weight on said opposite disc face, said weight having slots therethrough for the subdivision thereof into a plurality of counterweight masses corresponding in number to and respectively opposed from said plurality of separate plate elements.

5. Apparatus as claimed in claim 3 in which a plurality of separate plate elements are mounted on said adjacent faces of said discs, and wherein said counterweight means comprises an annular counterbalancing weight on each said opposite disc face, each said weight 1 1 having slots therethrough for the subdivision thereof into a plurality of counterweight masses corresponding in number to and respectively opposed from the plurality of separate plate elements on the respective disc.

References Cited by the Examiner UNITED STATES PATENTS 12 2,216,611 10/40 Dirnm et a1. 24l298 X 2,344,504 3/44 Dotzer 24l-298X FOREIGN PATENTS 18,716 1901 Great Britain.

1. SPENCER OVERHOLSER, Primary Examiner.

JOHN C. CHRISTIE, Examiner. 

1. IN APPARATUS HAVING A ROTATING DISC ON ONE FACE OF WHICH ARE MOUNTED A PLURALITY OF SEPARATE PLATE ELEMENTS TO BE MAINTAINED IN CLOSE TOLERANCE SPACING RELATIVE TO A COOPERATING ELEMENT OF SAID APPARATUS AND IN WHICH SAID PLATE ELEMENTS TEND TO BE AXIALLY DEFLECTED OUT OF SAID CLOSE TOLERANCE SPACING, THE IMPROVEMENT WHICH COMPRISES COUNTERWEIGHT MEANS ON THE OPPOSITE FACE OF SAID DISC, SAID COUNTERWEIGHT MEANS COMPRISING AN ANNULAR SMOOTH-SURFACED COUNTERBALANCING WEIGHT ON SAID OPPOSITE DISC FACE, SAID WEIGHT HAVING SLOTS THERETHROUGH FOR THE SUBDIVISION THEREOF INTO A PLURALITY OF COUNTERWEIGHT MASSES CORRESPONDING IN NUMBER TO AND RESPECTIVELY OPPOSED FROM SAID SEPARATE PLATE ELEMENTS, SAID PLATE ELEMENTS AND SAID COUNTERWEIGHT MASSES GIVING RISE TO SUBSTANTIALLY EQUAL AND OPPOSITE CENTRIFUGAL FORCES DURING ROTATION THEREOF, THE CENTRIFUGAL FORCES ON THE COUNTERWEIGHT MASSES COUNTERACTING THE CENTRIFUGAL FORCES ON THE PLATE ELEMENTS TO PREVENT AXIAL DEFLECTION OF THE DISC DURING ROTATION THEREOF. 